This invention relates to gas turbine engines and, more particularly, to the support structure for variable compressor vanes in such engines.
In an aircraft gas turbine (jet) engine, air is drawn into the front of the engine, compressed by a shaft_mounted compressor, and mixed with fuel. The mixture is burned, and the hot exhaust gases are passed through a turbine mounted on the same shaft. The flow of combustion gas turns the turbine, which turns the shaft and provides power to the compressor and fan blades. The hot exhaust gases flow from the back of the engine, driving it and the aircraft forwardly.
The compressor at the front of the engine typically has a low-pressure section and a high-pressure section. In the highpressure section, the air is compressed by the combined action of radially extending compressor blades that rotate with the compressor shaft about the centerline of the engine, and radially extending compressor vanes that are not mounted on the compressor shaft and do not rotate about the centerline of the engine.
However, the compresor vanes may be mounted so that they may be controllably rotated about their own radially extending longitudinal axes to vaiy the angle of the compressor vane airfoil to the air flow. The control of the variable vanes aids in establishing the air pressure ratio and flow rate that is introduced into the combustor, responsive to the operating requirements of the engine and the altitude.
Each of the high-pressure compressor vanes includes an airfoil with a shaft support extending from each end of the airfoil. The shaft supports are rotatably mounted to the inner shroud and the outer case that define the air flow path. A bearing structure in the shroud and case, including bushing bearings and washer bearings, supports the vane and allows it to rotate. In current engines, the bearings must function at a temperature of about 700xc2x0 F. or above for extended periods of time. Existing bearings are typically made of a polyimide material reinforced with woven carbon fibers. These bearings are operable and are widely used. However, they are susceptible to erosion and oxidation damage. Further, it is expected that the existing bearings will not be operable with projected increases in compressor pressure ratio and service temperatures in future engines.
There is a need for improved variable gas turbine compressor vane structures. The present invention fulfills this need, and further provides related advantages.
The present invention provides a variable gas turbine compressor vane structure that is operable at compressor pressure ratios and service temperatures in excess of those experienced in existing engines. Additionally, the variable gas turbine compressor vane structure is more resistant to erosion and oxidation damage than are available structures. The approach of the present invention requires no change to the airfoil section of the compressor vanes or to their mode of operation.
A variable gas turbine compressor vane structure comprises a gas turbine compressor vane having a vane support at an end thereof, and a case structure comprising a bearing support disposed to engage the vane support of the gas turbine compressor vane. The bearing support comprises a metal skeleton having open-cell porosity extending therethrough, and an infiltrant material infiltrated into the porosity of the metal skeleton. Examples of bearing supports include an outer-case bearing bushing, an outer-case bearing washer, and an inner-shroud bearing bushing.
The metal skeleton has adequate porosity to allow the infiltrant material to penetrate the metal skeleton. The metal skeleton may be, for example, a sintered nickel-base alloy or superalloy. The metal skeleton provides structural strength for the bearing support. The infiltrant material may be, for example, an organic polymer such as a polyimide, a ceramic, or a metal with melting point less than that of the metal skeleton.
The present approach provides a porous metal bearing support skeleton, which is infiltrated with another material. In the case of the preferred polymer infiltrant, the polymer material provides a surface lubricant that is continually replenished with new polymer as the metal skeleton wears.
The bearing support is resistant to erosion and oxidation damage and is operable to higher temperatures than possible with conventional reinforced polymer bearing supports. Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.